1. Field of the Invention
This invention relates to an apparatus for creating, as by drilling, a hole in the earth, and more particularly, but not by way of limitation, to such an appparatus for drilling large diameter holes in the sea floor for receiving subsea equipment.
2. Setting of the Invention
Large diameter holes (e.g., greater than about 2 meters in diameter) are created in the sea floor to protect underwater blow-out preventers, Christmas trees, valving, etc., used with underwater oil and gas wells in ice-infested waters, shipping lanes, fishing areas, etc.; for the installation of large diameter construction piles on land and underwater in inland waters and offshore; offshore mining for minerals; for vent and production shafts in mining for tar sands, oil shale, coal, potash, and other minerals; recovering mine tailings from tailing ponds; and in habor benching. These large diameter holes are created by specialized drilling apparatus, such as described in U.S. Pat. No. 4,304,309. The apparatus of U.S. Pat. No. '309 includes a normally fixed upper section and a lower section rotatably mounted on the bottom of the upper section. Drive mechanisms rotate the lower section relative to the upper section. Disc cutters are rotatably mounted on the base of the lower section for cutting and moving material in an earth formation beneath the apparatus, and for directing the cut material towards the bottom center of the base of the lower sections. A transfer pipe mounted in the base of the lower section receives the cut material and feeds the cut material into a central discharge pipe, mounted in and extending upwardly from the upper section and in fluid communication with the transfer pipe.
In the past, if a drill bit and drillstring were to be used to drill or core the subterranean formations while the large diameter hole was being drilled, the drilling apparatus would first have to be raised and stowed. Further, in the event that cuttings, gravel, rocks, and the like blocked or clogged the central cuttings removal system of the apparatus, the entire drilling apparatus would have to be raised to clean out the cuttings removal system. There is a need for a large diameter drilling apparatus that can be used, have access into, and be cleaned without having to raise the entire drilling apparatus.